For this reason signers SHOULD NOT reuse selectors with new keys, and
SHOULD assign a new selector to each new signing key.
In other words, you want the Informative note to become Normative.
Does the additional normative language make the protocol work better or add a
protocol feature? I tend to expect one of those benefits from normative
text.
I think it makes the protocol work better, by removing a possible failure
mode in which the signature is good, but the validation key changed
between the time a message was signed and it was checked. Although it
would be rather dimwitted to do so, a signer with a severe fear of replay
could keep the same selector and change the keys under it, or maybe rotate
between two selectors with new keys each time.
R's,
John
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